Carbon nanostructures as fullerene, nanotubes, and graphene have been widely used to reinforce different inorganic matrices (e.g. polymers (organic, inorganic and bio-), metals, concretes, ceramics, etc.) thus producing composites with improved mechanical or multifunctional properties. The most common polymer matrices include, epoxy, polyester, polyvinyl, pure carbon (graphene, amorphous, graphitic), polyethylene, etc. Carbon nanotubes have demonstrated mechanical improvements on polymers matrix composites such as strength, toughness, elongation, Young's modulus, wear. Further improvements are reported on conductivity, in both DC and AC modes. Proper functionalization of carbon nanostructures provides further enhancement of the mechanical properties of composites. In polymers, the interactions (i.e. chemical) among the reinforcement and matrix may result in further enhancement of the mechanical properties. Carbon particles (e.g. nanotubes or graphenes) can be the key to trigger polymeric matrices with multi-functional character for manufacturing of lightweight components for advanced applications (aerospace, electronics, automotive etc.). However, the literature highlights that a serious limitation in this type of composites is represented by the inefficient dispersion of the nanotubes in the host matrix.
Several efforts had been conducted to reinforce composites with carbon for decades. Carbon-carbon composites were first developed by introducing fibers in carbonaceous matrices known for their exceptional thermal shocks, wear, ablation, toughness, high temperature, and friction resistant properties. The fibers have strengths of up to 4 times that of advanced steels (up to 4 GPa). These composites are useful for aerospace, defense among other applications. Traditionally, the synthesis of carbon nanostructures (fullerene, nanotubes and graphene) is conducted by evaporation of carbon. Those carbon nanostructures are known for their outstanding mechanical electrical and thermal characteristics. The carbon nanotube opened new horizons for structural materials to reinforce textiles, polymers, metals and ceramics. On those early stages the hardness in metallic matrices had been improved in up to 800%. More recent reports show toughness improvements in ceramic matrix composites between 300% and 500% with electrical property improvements of more than 12 orders of magnitude.
The development of carbon nanostructures to reinforce composites is a strategy for producing a new generation of materials with superior mechanical properties. Carbon nanotubes are the most investigated particles with positive results. However, the improvements in mechanical properties are below theoretical expectations. Similar results are found with graphene. The scientific community has been using pristine quality carbon nanostructures to reinforce composites. Pristine quality carbon nanostructures possess outstanding properties; unfortunately, these properties are affected by the particle's integrity thereby limiting choice of manufacturing methods. Further, carbon nanotubes have discrete reinforcement effects. In order to achieve effective reinforcement it is necessary to develop an interconnected network of the reinforcement that guarantee intimate interaction with the matrix. The ideal carbon reinforcement should possess the following characteristics: 1) large surface area, 2) malleability, 3) resistance to thermo mechanical processing, 4) limited reactivity with the matrix, 4) easy to synthesize and manipulate, 5) in situ transformations into nanotubes, fibers, etc., and 6) potential for mass production and cost effective. From the above list the most important properties are mass production and the particle's ability to transform in situ in order to guarantee effective reinforcement.